It is known (see for example Industrie-Anzeiger No. V, 10 May 1966) to form a hollow metal part by confining a piece of metal tubing in a die having an inner surface corresponding to the outer surface of the part to be produced, with the ends of the tube exposed. Respective rams are pressed against the tube ends and hydraulic fluid at very great pressure, in excess of 1000 kp/mm.sup.2, is fed in through one of the rams to the interior of the tube. The combined axial compression and internal pressurization cause the tube to expand radially to fill the die cavity, producing an accurately dimensioned cold-machined part.
Changeover from one product to another with such a manufacturing method is quite onerous. Clearly the die must be changed. In addition it is standard practice to change the pistons and rams also. This necessitates undoing complex hydraulic hookups and entails substantial down time.